Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 010752
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
352 AM EDT SUN MAY 1 2016

.SYNOPSIS...
A WAVY FRONTAL BOUNDARY ACROSS THE REGION THIS MORNING IS EXPECTED
TO LIFT NORTH AS A WARM FRONT TODAY. MEANWHILE...A SLOW MOVING COLD
FRONT APPROACHING FROM THE WEST WILL KEEP A WARM AND HUMID AIR MASS
ACROSS THE REGION THROUGH MONDAY AND MONDAY NIGHT. THE FRONT WILL
FINALLY MOVE ACROSS THE REGION ON TUESDAY. A SECOND STRONGER COLD
FRONT WILL PASS ON THURSDAY AND WILL BRING DOWN A MASS OF COLD AIR
FROM CANADA FOR LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM EDT SUNDAY...A BUSY EARLY MORNING ACROSS THE WESTERN
CAROLINAS AND NORTHEAST GEORGIA AS A SHORT WAVE MOVING ACROSS THE
REGION CONTINUES TO PROVIDE A FAVORABLE ENVIRONMENT FOR THE
DEVELOPMENT OF SHOWERS AND THUNDERSTORMS DEVELOPING NEAR A WAVY
PSEUDO-WEDGE BOUNDARY ACROSS THE MOUNTAINS AND NORTHEAST GA. THIS
WILL REQUIRE A LIKELY/CATEGORICAL POP ACROSS MUCH OF THE MTNS AND
FOOTHILLS THROUGH SUNRISE. FORTUNATELY...THE HEAVY RAIN IS EXPECTED
TO AVOID THE SRN PART OF METRO CLT WHERE FLOODING RAIN OCCURRED
SATURDAY EVENING. TEMPS WILL REMAIN MILD.

MORE UNCERTAINTY THAN USUAL THIS MORNING REGARDING THE FCST FOR THE
NEXT 12-24 HOURS...COMPLICATED BY THE REMNANT WEDGE/COOL POOL FROM
EXTENSIVE CONVECTION OVER THE PREVIOUS 12-18 HOURS OR SO. WE WILL
REMAIN IN A SW FLOW ALOFT WITH PLENTY OF LOW LEVEL MOISTURE IN
PLACE. THE PASSAGE OF THE AFOREMENTIONED WAVE MAY PROVIDE FOR A BIT
OF A LULL IN THE ACTION IN THE MID/LATE MORNING ALTHO THE FCST DOES
NOT INDICATE IT AS SUCH...OWING TO CONTINUITY WITH THE PREVIOUS FCST
AND THE ENSEMBLE GUIDANCE. ULTIMATELY...THE CONVECTION ALLOWING
MODEL GUIDANCE MIGHT HAVE THE BEST HANDLE ON THE SITUATION...
SUGGESTING THE LULL AND A LOWER POP DURING MID-MORNING. THEN IT
BECOMES A MATTER OF HOW MUCH WE WILL DESTABILIZE LATER IN THE
DAY...KNOWING WE HAVE A REMNANT COOL POOL AND EXTENSIVE DEBRIS
CLOUDS. SUSPECT THE NAM IS OVERDONE...PERHAPS BY A FACTOR OF
TWO...AND AM IN FAVOR OF THE GFS IN KEEPING SBCAPE MORE IN THE 1000
- 1500 J/KG RANGE. HOPE THE NAM IS OVERDONE BECAUSE OTHERWISE WE
MIGHT SEE SOME WELL-ORGANIZED DEEP CONVECTION WITH ENOUGH
SHEAR/HELICITY TO WORRY ABOUT SUPERCELLS. INSTEAD...THINK MOST
STORMS WILL BE MORE GARDEN-VARIETY AND THE BETTER CONVECTION WILL BE
TO OUR NW CLOSER TO THE MIDDLE OF THE MARGINAL RISK IN THE DAY 1
CONVECTIVE OUTLOOK FROM SPC. WOULD NOT RULE OUT A FEW SEVERE
STORMS...BUT WILL ALSO HAVE TO KEEP AN EYE ON FLASH FLOOD POTENTIAL.
TEMPS WILL SEE A REBOUND OVER THE NW PIEDMONT...BUT WILL BE CLOSE TO
YESTERDAY ELSEWHERE. THE GUIDANCE SUGGESTS THAT PRECIP CHANCES WILL
DIMINISH AFTER SUNSET AND THE FCST WAS NUDGED IN THAT DIRECTION WITH
PRECIP PROBABILITY LOWERED IN THE LATE AFTERNOON...AND CONTINUING TO
TAPER OFF OVERNIGHT. LOWS WILL REMAIN SEASONALLY MILD.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300AM EDT SUNDAY...CHANCES FOR THUNDERSTORMS CONTINUE ON
MONDAY AS SOUTHWESTERLY BOUNDARY LAYER FLOW PERSISTS AROUND A
SURFACE TROUGH WEST OF THE APPALACHIANS AHEAD OF AN UPPER CENTRAL
CONUS TROUGH THAT MAKES GRADUAL EASTWARD PROGRESS.  MONDAY AFTERNOON
SOUNDINGS SHOW PWATS AROUND 1.5 INCHES...MODEST INSTABILITY...AND
MODEST BULKSHEAR...CONDITIONS SIMILAR TO SATURDAY AND SUNDAY.
RESULT WILL BE CONTINUED CHANCES FOR THUNDERSTORMS ON MONDAY WITH
THE POTENTIAL FOR LOW-END SEVERE AND LOCAL FLOODING IF CELLS SHOULD
TRAIN OVER ONE AREA.

TROUGH REACHES THE CWA WITH A COLD FRONT AS UPPER SYSTEM CONTINUES
TO PROGRESS MONDAY NIGHT.  LIGHTER NON-THUNDER SHOWERS MAY PERSIST
TUESDAY MORNING...DESPITE DECLINING PWATS...DUE TO FORCING FROM
UPPER SYSTEM.  SOME UPSLOPE SHOWERS ON THE WEST SIDE OF THE
MOUNTAINS MAY ALSO CONTINUE INTO TUESDAY...BUT TUESDAY WILL HAVE
MOSTLY DRYER CONDITIONS AND AN END TO RAINFALL.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 300AM SUNDAY...FOLLOWING PASSAGE OF MAJOR FRONT EARLY
TUESDAY...MOISTURE PLUMMETS ACROSS THE AREA AND SIGNIFICANT
ADDITIONAL PRECIP IS NOT EXPECTED WEDNESDAY THROUGH SATURDAY.
TEMPERATURES ALSO DECLINE TO 5 TO 10 DEGREES BELOW NORMAL.  SOME
ISOLATED RAIN SHOWERS...AND POSSIBLY EVEN AN ISOLATED THUNDERSHOWER
ARE POSSIBLE...ESPECIALLY WEDNESDAY AFTERNOON WHEN MODELS HAVE A
SHORTWAVE TRAVERSING THE AREA BUT GREATLY REDUCED BL MOISTURE LIMITS
POTENTIAL.

IN ADDITION TO SHORTWAVES ROTATING AROUND MAJOR UPPER TROUGH
DEVELOPING OVER THE NORTHEAST CONUS...MODELS CONTINUE TO SHOW A SHOT
OF COOL CANADIAN AIR DESCENDING WITH THIS UPPER TROUGH WITH A MAJOR
COLD FROPA ON THURSDAY...AND THE COLDEST POINT IN THE FORECAST BEING
REACHED FRIDAY MORNING.  GFS STILL HAS 850MB TEMPS DOWN TO -2C OVER
THE MOUNTAINS BEHIND THE FRONT...WITH THE EC SLIGHTLY WARMER AT
-1C.  FRONT COULD GENERATE SOME LIGHT SHOWERS...ESPECIALLY WITH
UPSLOPE ENHANCEMENT ON THE WEST SLOPE OF THE MOUNTAINS...BUT SURFACE
TEMPERATURES SHOULD BE JUST WARM ENOUGH EVERYWHERE TO STILL PRECLUDE
ANY WINTER PRECIP. TYPES.  GFS-EC AGREEMENT IS QUITE GOOD THROUGH
THURSDAY...INCLUDING DETAILS ABOUT SHORTWAVE PASSAGE ON WEDNESDAY.
COOL AIR INTRUSION FRIDAY IS SEASONALLY SHORT-LIVED WITH
TEMPERATURES REBOUNDING TO NORMAL SATURDAY AFTERNOON.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...A MIXED BAG FOR THE REST OF THE OVERNIGHT
AND PROBABLY THROUGH THE MID-MORNING HOURS WITH VARIABLE CEILING AND
VISIBILITY DEPENDING ON LOCATION RELATIVE TO WAVES OF SHOWERS
EXPECTED TO MOVE ACROSS THE REGION. MOST PLACES WILL BE MVFR OR
IFR/LIFR THROUGH THAT TIME...WITH THE THOUGHT THAT IFR WILL
EVENTUALLY PREVAIL AFTER CURRENT BAND OF LIGHT PRECIP MOVES EAST.
THINK THE BIGGER PROBLEM WILL BE CEILING AND NOT VISIBILITY.
MEANWHILE...THERE WILL BE SOME VFR HOLES IN THE LOW CLOUD CEILING.
WIND GENERALLY SHOULD BE SE TO THE SOUTH OF AN OLD BOUNDARY RUNNING
ROUGHLY ALONG I-85...AND NORTHEAST TO THE NORTH OF THE BOUNDARY.
THIS IS EXPECTED TO WASH OUT WITH SE WIND TAKING SHAPE AT ALL PLACES
BY SUNRISE. UNCERTAINTY ABOUNDS FROM SUNRISE ONWARD ABOUT WHEN
SHOWERS/THUNDERSTORMS WILL OCCUR. THE LATEST GUIDANCE FROM
CONVECTION ALLOWING MODELS SUGGESTS IT WILL ACTUALLY BE A FAIRLY
QUIET DAY...BUT THIS TREND WAS NOT FOLLOWED YET. INSTEAD...HIT THE
AFTERNOON TSRA CHANCE WITH A PROB30 OR TEMPO AT ALL SITES. ENDED
PRECIP/RESTRICTION THREAT EVERYWHERE BY 00Z BASED ON GUIDANCE
SHOWING A WAVE MOVING PAST AROUND THAT TIME. MOST DETAIL BEYOND 00Z
MONDAY WAS ELIMINATED FOR BREVITY.

OUTLOOK...UNSETTLED WEATHER/OCCASIONAL CONVECTION/RESTRICTIONS ARE
EXPECTED TO CONTINUE INTO EARLY NEXT WEEK...AS A FRONT BECOMES
STALLED NEAR THE AREA. DEFINITIVE DRYING DOES NOT APPEAR LIKELY
UNTIL AT LEAST MID-WEEK.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       MED   77%     HIGH  81%     HIGH  92%     HIGH 100%
KGSP       MED   68%     HIGH  87%     HIGH 100%     HIGH 100%
KAVL       MED   76%     HIGH  86%     HIGH  97%     MED   73%
KHKY       LOW   54%     MED   63%     HIGH  94%     HIGH  93%
KGMU       MED   77%     HIGH  89%     HIGH 100%     HIGH 100%
KAND       HIGH  81%     HIGH  87%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...PM
NEAR TERM...CDG/PM
SHORT TERM...WJM
LONG TERM...WJM
AVIATION...PM


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